The subject matter of this application relates to the subject matter of concurrently filed application Ser. No. 085,151, filed Oct. 15, 1979, now U.S. Pat. No. 4,445,532 entitled "Solenoid Valve Assembly".
This invention relates to pressure regulator systems for providing a relatively low regulated fluid pressure output from a relatively high pressure fluid source. In one embodiment of the invention, the pressure regulator system is adapted for use as a pressure activated starting system for a gas turbine machine.
Gas turbine machines require for starting purposes a supply of pressurized fluid for initiating rotation of a turbo-compressor rotating group. Specifically, the rotating group must be accelerated to a minimum threshold speed for continued self-sustained operation of the gas turbine machine. In the prior art, one common source of pressurized starting fluid for gas turbine machines such as auxiliary power units for aircraft and the like comprises stored or bottled compressed air.
In some applications, a self-contained starting system is desirable wherein a relatively small and lightweight source of starting fluid is carried with the engine and is recharged by operation of the engine so as to allow the engine to be started whenever and wherever desired. See, for example, U.S. Pat. No. 4,068,468. In these self-contained systems, pressurized fluid is supplied from a reservoir tank through a pressure reduction regulator to the compressor of the turbo-compressor rotating group, or alternately, to a rotating starting motor. Once the gas turbine machine has reached self-sustaining operation, the reservoir is conveniently replenished with bleed air from the compressor so as to recharge the starting system for subsequent starting of the engine.
A major design difficulty in pneumatic self-contained starting systems arises in that substantial quantities of compressed fluid are required for starting the gas turbine machine. Accordingly, the reservoir is required to contain a substantial quantity of pressurized fluid for starting purposes. To reduce the size of the reservoir carried with the machine, the reservoir commonly contains this fluid at a relatively high pressure, say on the order of about 4,000 p.s.i. At these pressure levels, substantial pressure reduction through the pressure reduction regulator to say about 400 p.s.i. is necessary prior to supply of the fluid to the gas turbine machine for starting. This substantial pressure reduction results in transonic fluid flow through the pressure reduction regulator which correspondingly results in sonic shock waves and shock wave feedback whereby the regulator flow is highly irregular and unstable. It is therefore desirable to provide an improved pressure reduction regulator for use in applications such as self-contained pneumatic starting systems for providing substantial pressure reduction while at the same time assuring accurate and stable transonic flow therethrough.
A variety of other types of systems experience similar flow stability problems stemming from the reduction of a relatively high pressure fluid source to a relatively low regulated pressure fluid output. For example, pneumatic gun drives are known wherein it is necessary to reduce a high pressure fluid source of about 10,000-12,000 p.s.i. to a regulated pressure level of a few hundred p.s.i. In these other types of systems, similar fluid flow shock effects and the like are encountered resulting in a highly irregular and unstable fluid output pressure.
Another area of design difficulty in prior art pressure regulator systems comprises the operating characteristics of the control valve utilized to initiate supply of the high pressure fluid to the pressure reduction regulator. This valve typically comprises an electrically actuated solenoid valve including a valve member subjected to the relatively high pressure level of the pressurized fluid source. Accordingly, the solenoid valve must develop relatively high opening forces to overcome the pressure forces of the fluid source, and thereby initiate actuation of the system. However, it is well known that solenoid valves inherently develop increased force capacity throughout stroke of the associated valve member, whereas in this environment a maximum opening force is required in the initial stage of the valve member stroke. Therefore, in the prior art, a relatively expensive and oversized solenoid valve has been used so as to assure adequate opening forces upon initial stroke movement of the valve member. In the prior art some systems have attempted to overcome the solenoid size design problems by using a so-called impact solenoid valve wherein an armature is designed for limited lost motion movement prior to impacting a valve member. In this manner, the solenoid valve operates only through the latter, higher force portions of the stroke. See, for example, U.S. Pat. Nos. 2,612,188; 2,735,644; 3,043,336; 3,450,353; 3,473,380 and 3,974,998. However, these impact solenoid designs have not maximized the capacity of a relatively small and inexpensive solenoid valve to open a valve member to initiate actuation of the pressure regulator system.
The present invention overcomes the problems and disadvantages of the prior art by providing an improved pressure regulator system including a pressure reduction regulator for providing accurate flow and pressure under transonic flow conditions, and an improved solenoid valve assembly for maximizing the opening force capacity of a solenoid valve member.